Meiosis, DNA Replication, and Chromosomal Abnormalities

Comprehensive vocabulary flashcards covering the processes of meiosis, DNA replication, crossing over, chromosomal non-disjunction, syndromes, and karyotyping based on lecture notes.

Chromosomes

Long, thread-like structures that form a chromatin network in nuclei, made up of a DNA strand wound around histone proteins.

Somatic cells

Body cells that have the same number of chromosomes in each cell, containing two sets (maternal and paternal).

Homologous pair

A pair of chromosomes = one matching paternal and one maternal chromosome of the same size and shape, carrying the same genes at the same loci.

Centromere

Joins 2 identical chromatids during interphase.

Meiosis

Cell division in reproductive organs to produce gametes (or spores in plants), halving the chromosome number from two sets to one set (haploid).

Haploid

Cells (gametes) that contain only one chromosome from each homologous pair.

Diploid zygote

Formed when a male haploid gamete fuses with a female haploid gamete.

Microsporangia

Pollen sacs in the anthers where spore formation occurs during meiosis.

Megasporangia

Ovules in the ovaries where spore formation occurs during meiosis.

DNA replication

1. DNA unwinds + unzips (weak hydrogen bonds break) = 2 strands

2. Free floating DNA nucleotides join complem DNA nucleotides

3. hydrogen bonds reform

4. DNA rewinds + re-zips = 2 identical strands

5. Identical copy = genetic code passed to each new daughter cell

Prophase I

1. Homologous chromosomes = side by side = bivalent

2. Nuclear membrane disintegrates

3. centrosome spilts & centrioles move to opp poles

Synapsis

The pairing of replicated homologous chromosomes to form bivalents during prophase I.

Crossing over

The exchange of genetic material between inner chromatids of homologous chromosomes by breaking and reforming DNA during prophase I.

Chiasmata

The points of contact where crossing over takes place

Recombinant chromatids

Genes from maternal chromatid swap w genes from paternal chromatid

Parental chromatids

Chromatids that did not exchange genetic material during crossing over.

Metaphase I

1. Bivalents move to the middle in a random arrangement

2. Centromeres attach to spindle fibres.

Anaphase I

Centromeres do not split but bivalents separate and chromosomes are pulled to opposite poles by spindle fibres.

Telophase I

1. Cytoplasm divides (cytokinesis) = haploid cells

2. Nuclear membranes reform

3. Spindle fibres disappear

Meiosis II

The second division where each haploid cell divides by mitosis to separate chromatids = four haploid daughter cells.

Meiosis importance

1. Forms gametes

2. chromosomes halved = same gen to gen

3. genetic variation

Chromosome non-disjunction

Chromosomes don’t separate properly during meiosis = gametes with extra or missing chromosomes.

Aneuploidy

A condition where a zygote has an abnormal number of chromosomes due to fertilization of an abnormal gamete.

Klinefelter's syndrome

An aneuploidy condition when a boy is born with an extra sex chromosome = sex chromosomes did not separate properly = sparse body hair, enlarged breasts, and small testicles and penis.

Down syndrome

An aneuploidy condition (trisomy $21$) =$47$ chromosomes per cell, caused by non-disjunction during oogenesis leading to three copies of chromosome number $21$.

Amniocentesis

Determine a karyotype.

Karyotype

Complete set of chromosomes displaying their number, size, and shape during metaphase of mitosis, used to determine sex and identify chromosomal abnormalities.

Autosomes

The $22$ pairs of non-sex chromosomes.

Gonosomes

The sex chromosomes ($X$ and $Y$)